The most forgiving Callaway X Hot irons produce faster ball speeds

In the X Hot irons, Callaway takes the "Speed Frame Face Technology" it's been using in its drivers and utilized it in irons. That tech is designed to create a better transfer of energy from clubface to golf ball, thereby boosting ball speed and distance performance.
These irons also use a Deep Undercut Cavity design to move the center of gravity lower (helping with launch) and move the "hottest" part of the clubface lower, as well.
The X Hot irons also incorporate "Feel Management Technology" in the back of the clubhead, for crisper feel and sound.